Abstract

Cytokinesis physically cleaves a cell into two through the assembly and constriction of an actomyosin ring. This process is crucial for growth and development, and the core machinery is highly conserved across metazoans. Studies in different systems have shown that both spindle-dependent and -independent mechanisms control this machinery. However, these mechanisms appear to vary widely among organisms and cell types. In addition, most of our knowledge of cytokinesis has been generated using only a couple of transformed cell types cultured in vitro, or in early embryos before cells adopt fates. This raises the question of how cytokinesis is regulated in diverse cell types and developmental contexts. This thesis characterizes cytokinesis in cells with different fates in C. elegans, and in mammalian cultured cell lines that have not been studied in this context before. In Chapter 2, we provide the first in-depth description of cytokinesis in AB and P1 cells with different fates in the two-cell C. elegans embryo. We found that each cell type has unique cytokinesis kinetics, driven by different thresholds of myosin. Our results revealed that cell fate, size and/or ploidy are contributing factors that regulate myosin levels and/or organization to influence these kinetics. We also demonstrated how a chromatin-dependent mechanism regulates cytokinesis differently in the two cell types. In Chapter 3, we compare cytokinesis kinetics for the first time in 5 different cultured mammalian cell types by studying the localization of endogenously tagged machinery. We found that this machinery has distinct spatiotemporal localization which reflects differences in cytokinesis kinetics among the cell types. Overall, this thesis highlights the diversity in cytokinesis and cytokinesis regulation, and explores the criteria that should be considered when conducting or interpreting cytokinesis research.